From U.S. Pat. No. 7,023,105 a method for controlling a wind turbine having an electric generator using air density data at the location of the wind turbine is known. In the method the generator of the wind turbine is controlled via a control unit which processes the air density data, and performance data for the generator are adjusted on the basis of the air density. In the known method, the elevation of the site of the wind turbine above sea level is taken into account, whereby the lower air density is taken into account in the power curve. Thus, the power to be generated by the wind turbine, which power is associated with a rotor rotational speed and thus with a particular tip speed ratio, can be adapted correspondingly, that is to say reduced, so that the generator torque does not exceed the torque provided by means of the generator as a result of exciting power supplied by the control unit. Overall, the aim is to maintain the efficiency determined via the power curve and to obtain the maximum amount of energy from the wind.
From U.S. Pat. No. 7,420,289 a method for calculating a power curve for high altitude sites is known. Therein, a relationship between the power coefficient Cp and the tip speed ratio λ is taken as a basis for determining a ratio between the electric output power P and the wind speed v.
From United States patent application publication 2008/0112807 a wind turbine is known in which the output power is reduced when the temperature of the ambient air drops below a predetermined threshold value. The reason for the power reduction is that at temperatures below −20° C. the operation of the wind turbine can require different load calculations.
In relation to the effects of the air density on the yield of the wind turbine, it should be borne in mind that in pitch-controlled wind turbines, a change in the air conditions can lead to aerodynamic stall effects with undesirable flow separation.